How do you solve the percentage change problem?

Hint: Before solving this problem we should know about what percentage change actually means.
Percentage change: it is a simple mathematical concept that represents the degree of change over time. It is used in many purposes like finance, is also used to represent the price change of a security.

Complete step-by-step answer:
Let we have a number and after some time there is change in number so we can calculate the percentage change in that number by following below mention:
Calculate the percentage increase:
Calculate the difference (increase) between the two numbers we are comparing.
  $ increase = New\,number - Original\,number $
After that, divide the increase by the original number then multiply the answer by 100. We get,
  $ \% increase = \dfrac{{Increase}}{{Original\,Number}} \times 100 $
If their answer is negative then, this is a percentage decrease.
Calculate the percentage decrease:
Calculate the difference (decrease) between the two numbers we are comparing.
  $ decrease = New\,number - Original\,number $
After that, divide the increase by the original number then multiply the answer by 100. We get,
  $ \% increase = \dfrac{{decrease}}{{Original\,Number}} \times 100 $
If their answer is negative then, this is a percentage increase.
So, by following this step we can calculate percentage change for any given problem.

Note: We use percentage increase or decrease to compare the quantity of a period of time. When the value of quantity is reduced, it is termed as depreciation and when value rises, it is called appreciation.